In Patent Document 1 (Japanese Patent Application Laid-Open (JP-A) No. 2016-078668), a vehicle seat including a seat back in which an elastic member is stretched between a left and right pair of side portions (for example, seat frame portions), in which a seat frame is covered with a soft pad material, such as foamed urethane or the like, and a seat cover, and in which a backing portion is configured by the elastic member, is disclosed. A side airbag device is accommodated at the side portion at the width direction outer side of the vehicle seat.
A structure in which a seat back movable portion that supports an upper body of an occupant is supported so as to be rotatable in a left-right direction bout an upper portion thereof is described in Patent Document 2 (Japanese Patent Application Laid-Open (JP-A) No. 2015-047973). Further, a structure in which a seating face support shape of a seat back pad is made to be changeable in accordance with a change in a support posture of a seated occupant is described in Patent Document 3 (Japanese Patent Application Laid-Open (JP-A) No. 2015-009605).
In the structure described in Patent Document 1 (Japanese Patent Application Laid-Open (JP-A) No. 2016-078668), even in a case in which a rotation force acts on an occupant at a time when a vehicle travels while turning, the occupant can be suitably supported due to a support face of the occupant moving according to expansion and contraction of the backing portion. However, in the structure described in Patent Document 1, since the occupant is supported by the backing portion at the time of a vehicle side impact, there is room for improvement in terms of increase in initial stage restraining performance for the occupant.